1. Field of the Invention
The present invention relates to a portable electronic device such as a lap-top type personal computer or wordprocessor and, more particularly, to a device having a memory card unit.
2. Description of the Related Art
In recent years, portable electronic devices such as lap-top type personal computers and wordprocessors have been developed. Some devices have memory card units in addition to floppy disk drives (FDDs) as external memories. In such a device, a memory card unit is stored in a housing of the device, and a memory card used as a memory medium is inserted into the memory card unit. The memory card serves as an external memory. The memory card has a housing, and the housing has a card base consisting of a plastic plate-like member. A memory circuit consisting of integrated circuits (LSIs) is mounted on the card base. A plurality of terminals (i.e., a connector consisting of contact holes) electrically connected to the memory circuit is arranged at the distal end portion of the card base.
The memory card unit has a box-like case for holding a memory card inserted into a card slot formed in a case unit constituting the housing of the device A connector corresponding to the plurality of terminals of the memory card is arranged in the box-like case. The connector is electrically connected to a predetermined circuit (external memory control circuit) on a printed circuit board to electrically connect the memory card to the printed circuit board.
The memory card may be erroneously inserted upside down into the memory card unit through the card slot. In this case, i.e., in an abnormal insertion state, the plurality of terminals arranged at the distal end portion of the memory card are electrically connected to the connector of the unit. When the card is inserted upside down as described above, the terminals of the memory card are not connected to the predetermined terminals of the connector but to other terminals. For this reason, for example, an abnormal circuit is formed by connections of a high-voltage power source terminal of the connector and a data input/output (I/O) terminal of the memory card. In this abnormal circuit, an abnormal current flows in a memory circuit of the memory card or a circuit (e.g., a data processing circuit mounted on the printed circuit board) on the housing of the device, and one or both of the memory circuit and the circuit on the housing of the device may malfunction.
In the device having the memory card unit as described above, the memory capacity of the memory card is smaller than that of a disk used in the FDD. For this reason, it is not so advantageous to use a memory card as an external memory medium in place of an FDD disk in practice. The memory cards have been used in application fields which require a small memory capacity and have limited operating conditions.